Reflector.



R. D. GRAY.

BEPLEGTOB.

APrLIoATIoN FILED Mmm, 1914.

Patented Mar. 30,1915.

5m ar@ ROBERT D. GRAY, 0F BIDG'EWOOD, NEW JERSEY.

' RE'FLECTOR.

`Specification of Letters Patent.

Patented Mar. 30, 1915.

Application led March 21, 1914. Serial No. 826,368.

To all whom t may concern:

Be it known that I, `ROBERT D. GRAY, a citizen of the United States, residing at Ridgewood, in the county of Bergen and State of New Jersey, have invented new and useful Improvements in Reflectors, of Which the following is a specification.

The present invention relates to reflectors for reflecting all the light issuing from an illuminant,and it is constructed on the principle that the normal at anyv point of an ellipse bisects the angle formed by the focal radii.l

Heretofore, it has been proposed to use a parabolic reflector for reflecting all the light issuing from an illuminant. With this type of reflector the reflected rays of light issuing from the illuminant in the focus of the reflector and falling onto the reflecting surface, are reflected in lines parallel to theaxis of the reflector. 'This direction of extension on the part ofthe reflected rays with respect to the axis of the reflector, is due tothe fact that the normal to a parabola at any point, bisects the angle between the focal radius and the line drawn'through the point parallel to the axis, or in other words, the normal to the point of incidence of any ray issuing from the illuminant and falling onto the reflecting surface, makes equal angles with the incident and reflected rays. As a consequence of this, it will be obvious, that maximum efficiency of a parabolic reflector can be had only in instances where the surface onto which it is desired to direct the reflected beam, is as large or larger than the cross sectional area of the largest partof the reflector.

effect of the light rays immediately beyond the said surface is not had or. the same. Therefore, a parabolic reflector 'is undesirable in instances where it is desired to obtain Y the maximum efficiency of a relatiyly'large reflector on a relatively small surface. Now

by virtue of that property of an ellipse asl hereinbefore stated, it is evident that 'with an elliptical reflector a ray of light issuing from an illuminant in one of the foci of an elliptical reflector and falling onto the reflector, is reflected in a line oblique to the Ifl the said surface be smaller than the open end of the reflector, then the bisect the angle formed by the focal radii as hereinbefore stated.

Having thus stated the properties upon which depend 'the uses of ,parabolic reflectors and elliptical reflectors, and pointed out wherein each type differs from the other in point of direction of extension of the reflected rays, I now come to the present invention which has for its general object the adapting of the surface of a reflector to direct the rays of light reflected thereby in a direction oblique to the axis of the'reflector and onto a point in axial alinement with the illuminant or source 0f light. And to that end the present invention resides in providing anelliptical reflector and arranging an ,illumina-nt in the focus of this reflector so that the reflected rays will be directed in a direction obliquely to the axis of the reflector and onto a .point in alinement with the illuminant or onto the other focus'of the imaginary ellipse ofV which the reflector forms a part.

Other objects will appear and be better understood from that embodiment of my invention of which the following is aspecification, reference being had to the accompanying drawings forming part hereof, in which:-

Figure 1 is a perspective of the invention. Fig. 2 is a diagrammatic view showing the principle of the invention. Fig. 3 is a side elevation showing the invention in use.

In that embodiment of my invention shown in the drawings the reflector is indinently joinedtogtlrany-suitable manner, such as by rolling the meeting edge of one around the corresponding part of the other, as indicated by 7.

The reecting surface c on the interior of the casing b, may be of any approved construction and in section longitudinally of the casing thisv surface may be semi-elliptison cal in contour or may be constructed in con- 1 centric sect1ons each of which 1s tangent to,

an ellipse. For ordinary purposes the reflecting surface may be continuous as in the case of the ordinary parabolic reflector, but for a certain class of work which will be iid -hereinafter described, the reflecting surface used in connection with that work, will be planeand formed of concentric sections and this for'the purpose of obtaining reflected rays of equal focal length, which, as is wellknown,is impossible to obtain in the curvilinear type of reflector, on account ofthe aberrations invariably present there.

As shown the concentric rows'S-S which go to make up the reflecting surface, consistV each of a plurality of plane mirrors whose side-edges abutand are formed so as to fit nicely one against the otlier,\vhereby to avoid Y the presence of ordinary perceptible seams or'joints. The mirrors in one row are preferably arranged so as to break joint with those of an adjacent row, but if desired corresponding mirrors in the several rows may be made to aline. In either event, howposes of illustration, I have shown it as an incandescent electric lamp, which is arranged in a suitable socket 10 formed with the cas-A ing, which socket is provided with the usual switch button 11 for controlling the flow of current to the lamp and which is adaptede,

to receive the Wires of an electric circuit.

The structure thus shown and described vmay be used for any of the purposes required Aof an ordinary reflector but it is ideally adapted for photographic enlarging work. In the drawings I have shown the reflector in use with a photographic enlarging apparatus. Y VSuch aparatus is indicated by 12 and is adapted for containing the negative 13.V Here the reflector is provided with a suitable bracket 14 for securing it upright in a container 15 which is provided withY a ground glass 16. The lens system in the lens barrel 17 and the lamp are arranged in axial alinement and for such distances apart as to limit myself to this structure.-

form the foci of an ellipse as shown in Fig. 2 of the drawings. Consequently with this construction, the reflected rays of light are directed into the lens, as shown in the said Fig. 2.

part of a reflector of this type andwhen usediii connection with photographic ven- Inasmucli as maximum efficiency Von the Y Y la'rging apparatus, can be had only when the maximum number ofreflected rays are dif rected into the lens barrel, it is obvious that 'y in order to so reflect all the lightV withra Y mate in two dimensions, namely,-length and;`

plane. mirror such mirrorV should approxi? width, Vcorresponding dimensions fof .the Y,

flame, or asin the present instance, theinf candescent filament in the electric lamp'.V

Therefore, I preferably employ plane mirrors corresponding in surface area approxi' mately to the area of Vthe filament, but it,v

must me'understood that I doinot intend to What is claimed as new is: f

An apparatus .for vreflecting lightfrays soV that these will converge at a point remote 'n i fromrthe apparatus, and confiprisingacas-V ing -open at. one end and adapted'for con.-r taining Van lncandesc'ent Yelectric lamp and sfo supporting this lamp with its axis in aline-v ment with tliepoint on which the reflected rays converge, and a plurality of circularY f rows of plane mirrors arranged on thefinnerfy surface of thesaid casing,the` said'roWS being concentric and arrangedfone in front;Y of the otherwith the adiacent ends of'the `Y mirrors in each labutting, thek successive surfaces of'mirrors in adjacent rows being'arranged at tangents to a common semi-ellip tical curve, the mirrors in successive rows"v progressively increasing` in length fromthe inner end of the casing, and eachof such mirrors being proportioned in two dimen-V Y sions so as to correspond approximately lto the corresponding dimensions of the light image to be reflected thereby,

In testimony whereof I aflixmysigiiature in presence of twowitnesses. .l

VRoisiai'rrn. GRAY;

Witnesses: i f Y JOHN A. DONEGAN,VV y GEO. A. BYRNE. 

